J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment prebend

Are you sure about that Steve? Is the fulcrum not the headstay attachment up at the hounds?

Not to my understanding-with the mast butt max forward and headstay at class max (rig tune slack) my mast sits hard against the back of the partners, and my headstay is completely loose. So on my boat at least, the fulcrum is where the mast passes through the deck.

But-I think my numbers are off. I did the calc's a long time ago. I think the rig moves fore and aft at the hounds about 8" for every inch of movement on the cabin floor (sorry for the exxageration-I'm not an engineer). Still a significant difference though , as rig tension settings and headstay sag are dramatically impacted by fore and aft position of the hounds.

I know this from experience-my mast butt was frozen about 1 1/2" aft of the class measured position for the first several years that I had the boat. My rig had HUGE prebend and my boat was slow until I fixed the butt position (with a lot of effort) during the off season several years ago.

My headstay adjustment was off, At let out 3/4 inch that help alot.

Rob - Sorry I don't have any pics of this. When you pull your mast you'll see an oval that is screwed to the deck. The mast extrusion fits snug over this oval and prevents the mast base from moving. You should be able draw a line 1 inch back from the forward edge of the molded step the mast sits on. Measure the thickness of the mast extrusion and draw another line behind it. This is where the front of the oval that is screwed to the deck should be positioned. Once everything is reassembled, the distance from the forward edge of the mast to the forward edge of the molded step should be 1 inch for best class legal rig tuning.

Letting out the headstay 3/4" would increase the pre bend in the lower section.
It seems your backstay is too short and holding back the tip of the mast - On FW we had to add a 3" toggle to get enough slack - we always keep the sag in the backstay 3-4" and very rarely tension it below 15 knots.

With that much sag in the backstay don't you have trouble with the top main batten foully on the backstay? I all ready have that problem in light air. I'll have to measure the backstay when I winterize, but it seem a lot of the bend was in the top 1/3 of the mast. Easing the headstay reduced that bend.

With the amount of slack we have it's very easy to flip the backstay around the batten in the tack - besides our latest main does not have a full top batten.

I think my mast step is too far back.


http://img218.imageshack.us/my.php?image=dscn0472ap9.jpg

Yup!

What affect does my aft stepped mast have on sailability?

Will this be something I should move up on my priority list? Or no

I have constant 15 mph trades, would this help me in depowering the main with the backstay since its already bent back some? Or Is it just innefficient?.